Brenda, there are lots of great PB biographies for older kids. Teachers love them. I'd park myself in that section of the library and read, read, read, take notes particularly on the pacing, how they handle difficult topics (back matter). Our own Verla Kay has written several biographies in her cryptic rhyme style suitable for both younger and older children.
Check Highlight Foundation workshops and any classes offered locally too. I've just returned from the Carolinas SCBWI and went to a fantastic NF Biography workshop led by both an author and illustrator. I'm still consolidating my notes...stay tuned.